Two types of radiation damage can be detected: (1) alkali labile bonds and (2) enzyme sensitive sites (Endonuclease II of E. coli). The nature of the alkalilabile bond will be explored to determine whether it is due to base loss, to be tested enzymatically with the depurination enzyme, or to sugar damage. The half-life of a chemical species reactive with O2 and leading to an alkali labile bond will be determined. The chemical nature of the enzyme sensitive site will be investigated by enzymatic and chemical means. The kinetics of the repair of the different types of damage will be investigated in normal and transformed cell lines. The possibility that radiosensitizers create substrates for repair enzymes will be examined. Whether both types of damage are produced by hydroxyl radicals will be investigated.